TESTING OF A PRESIDENT: THE BACKGROUND; Strong at Politics, Weakened by Lapses

On Jan. 20, 1997, as an ebullient Bill Clinton took the oath of office for the second term that he hoped would secure his place in history, he returned to a theme that had been at the core of his claim to be a new kind of Democrat, declaring: ''Each and every one of us, in our own way, must assume personal responsibility, not only for ourselves and our families but for our neighbors and our nation.''

One year later, Mr. Clinton learned that Kenneth W. Starr, the Whitewater independent counsel, was investigating accusations that the President had started a sexual relationship with a White House intern in 1995 and then tried to cover it up.

Had the man who won the Presidency by speaking out for the people who ''play by the rules'' once more surrendered to a lifelong compulsion to bend and break them? Tonight, in the most painfully personal public confession of his life, and perhaps in American political life, Mr. Clinton was forced to acknowledge, in tight and reluctant tones, that he had.

''I must take complete responsibility for all my actions, both public and private,'' Mr. Clinton said, adding that he had answered ''questions about my private life, questions no American citizen would ever want to answer.''

How someone of such surpassing intellect and such protean political talents could indulge in such reckless conduct at a time when he knew a special prosecutor was already scrutinizing his Administration and when his own re-election still hung in the balance remains the most puzzling question about William Jefferson Clinton. But it is not a new question, and in some ways it was predictable that this President should have come to this pass, his promise once again shadowed by his shortcomings.

For Mr. Clinton has always been convinced that he could outsmart, out-talk, out-charm and outlast any adversary, and very often, enough to confirm that conviction, he has. In the darkest days of the 1992 primaries, he dared to campaign on a platform of personal responsibility, despite widespread questions about his own marital fidelity, marijuana use and draft record, and widespread doubt that his answers were candid or complete. In his first term, he shifted ground so many times that even his best friends sometimes said they did not know where he stood.

Time and again in the risky running melodrama of his public life, Mr. Clinton has treated the truth as an a la carte menu.

On Jan. 21, as news of the accusations involving Monica S. Lewinsky came out, Mr. Clinton told National Public Radio: ''I don't know any more about it than I've told you, and any more about it, really, than you do.''

Even tonight, Mr. Clinton insisted that when he testified under oath in January that he had not had a sexual relationship with Ms. Lewinsky, his answers were ''legally accurate,'' though he added: ''I did not volunteer information.''

In the end, such sweeping elisions of reality lie far beyond the ken of conventional political analysis. But professionals who have studied the arc of Mr. Clinton's life and career have suggested some answers.

''Most people wish to think well of themselves,'' wrote Stanley A. Renshon, a political scientist and psychoanalyst at New York University in his 1996 study of Mr. Clinton, ''High Hopes.'' ''However, Bill Clinton appears to have come to believe the best of himself and, either to avoid or discount evidence from his own behavior, that all is not as he believes it to be. He attributes to himself the most sincere and best of motives. His errors, when acknowledged, are the result of basically correct efforts gone temporarily awry, misunderstandings that, if one knew more of what he knew, would disappear or be mitigated, or else are attributable to naivete and inexperience.''

Mr. Clinton may have come by his capacity for denial and compartmentalization naturally. They were among the qualities that allowed his widowed mother, Virginia Kelley, to persevere after Mr. Clinton's father died three months before he was born, and that allowed Mr. Clinton to make what most critics regarded as a splendid State of the Union address just days after the intern scandal broke.

''When bad things do happen, I brainwash myself to put them out of my mind,'' Mrs. Kelley wrote in her autobiography, published after her death in 1994 under the President's review. ''Inside my head, I construct an airtight box. I keep inside it what I want to think about and everything else stays behind the walls. Inside is white, outside is black: The only gray I trust is the streak in my hair.''

But gray is Mr. Clinton's favorite weapon. It has been central to his successes and to his setbacks. As Governor of Arkansas and then as a Presidential candidate, he succeeded in blurring old distinctions of ideology, proclaiming himself neither liberal nor conservative but ''new.'' As President, he at first promised both a tax cut and new spending, then raised taxes instead. Two years later, he apologized for raising taxes too much, claiming that Congress had forced him to do so, a claim at sharp variance with the facts.

This is the man who pledged not to raise taxes ''to pay for my programs'' (he raised them to cut the deficit), who said he had never ''broken the laws of my country'' (he tried marijuana as a Rhodes Scholar in England), who defended his campaign finance practices by saying he had never ''changed Government policy solely because of a contribution.'' His reputation for shading the truth grew so encrusted that he faced semi-serious questions from reporters over trivial matters, from his golf scores to whether he really shot two ducks on a New Year's outing in Arkansas, or just carried some that were shot by others.

Many times, Mr. Clinton has accepted responsibility and forsaken blame. After his 1980 defeat after one term as Governor of Arkansas, his political consultant Dick Morris advised him to apologize for past mistakes, like raising taxes and car license fees. Mr. Clinton resisted repeated entreaties to say he was sorry, devising his own folksy formulation for a television commercial: ''When I was a boy, my daddy never had to whip me twice for the same thing.''

In fact, the only daddy Mr. Clinton knew was an alcoholic stepfather who sometimes beat his mother, not him. And the President has spent a great part of his life being whipped, often quite publicly, for repeating his own mistakes. In his very first run for office, in 1974, his girlfriend, Hillary Rodham, reportedly sent her father and brother to help on his Congressional campaign because she worried about the rumors of his multiple romances on the road.

In 1992, faced with accusations by Gennifer Flowers of a 12-year sexual affair, Mr. Clinton said, ''That allegation is false,'' acknowledged causing pain in his marriage and largely put to rest an issue that had derailed the 1988 campaign of Gary Hart. But under oath in his deposition in the Paula Corbin Jones civil suit this year, Mr. Clinton acknowledged sexual contact with Ms. Flowers.

Over the years, Mr. Clinton has occasionally articulated a personal hierarchy of relative wrongdoing, once blurting out in a conversation with reporters aboard Air Force One -- apropos of nothing -- that it was the money-changers in the temple who really made Jesus mad, not the adulterous woman, of whom Jesus said in the Book of John: ''He that is without sin among you, let him first cast a stone at her.''

Correction: August 20, 1998, Thursday An article on Tuesday about President Clinton's pattern of personal lapses misstated the affiliation of Stanley A. Renshon, author of ''High Hopes,'' a 1996 character study of the President. He is a psychoanalyst and professor of political science at the City University of New York, not at New York University.